This document relates generally to providing electrical power from a fuel-powered generator and particularly, but not by way of limitation, to a generator with DC boost for an uninterruptible power supply system or for enhanced load pickup.
Both businesses and households rely on electrical equipment powered from one-phase, two-phase, three-phase, or other suitable utility-provided alternating-current (AC) power sources. However, commercial power reliability may not suffice for certain applications, for example, for computer facilities, hospitals, banking systems, or industrial motor loads. Therefore, a backupxe2x80x94or even an independentxe2x80x94local power source may be desirable to provide a supplement to or substitute for a utility-provided AC power source.
One type of a local power source is a static system, which typically uses an inverter to generate the load""s AC power from a direct current (DC) battery bank. Providing power from such a static system for an extended period of time, however, may require a large and costly bank of batteries. Another type of local power source is a rotary system, which typically uses a gasoline or diesel engine to rotate the shaft of an AC generator to produce an AC load current for an extended period of time. In such a system, a providing a stable output voltage signal typically requires a constant rotational shaft velocity. However, load-switching, motor-starting, or other load variations may perturb shaft velocity and, in turn, may perturb the stability of the output voltage signal. A mechanical flywheel storing kinetic energy may assist in maintaining a constant shaft velocity may be maintained by storing kinetic energy, such as in a mechanical flywheel. However, this, provides a bulky, costly, and inefficient solution. For these and other reasons, the present inventor has recognized a need for an improved backup and/or substitute local AC power source.
A local power generation system generates a substantially DC voltage at an inverter input, which is modulated to generate a resulting output AC power signal to a load. The inverter input voltage may be obtained from an engine generator, providing an AC power signal that is rectified, or from a fuel cell generator providing a DC voltage that is converted to the desired voltage value at the inverter input. An energy storage device helps maintain the DC voltage when load power draw increases, until the engine (or fuel cell reaction) accelerates enough to accommodate the increased power demand. The system may also be used in an uninterruptible power supply (UPS) application, in which the load draws power from a utility-provided AC power source until a fault condition appears. When the fault condition appears, the load switches its power draw from the utility-provided AC power source to the inverter output. The energy storage device helps maintain the DC voltage at the inverter input until the generator (engine or fuel cell) starts and accelerates to a level sufficient provide the DC voltage. The system may also include switching devices for providing uninterruptible power to a critical load, while permitting a noncritical load to be subjected to a fault-condition on the utility-provided AC power signal for a short period of time, before switching to receive power from the inverter output.
In one example, this document discusses a system providing AC electrical power to a first load includes a generator. An inverter includes an inverter input coupled to the generator output and an inverter output adapted to be coupled to the first load device. The system also includes an energy storage device and a first DC-to-DC converter circuit. An input of the first converter is coupled to the energy storage device. An output of the first converter is coupled to the inverter input. An energy supply circuit provides an energy supply circuit output coupled to the energy storage device. The energy supply circuit input is coupled to a power source selected from at least one of a utility-provided AC power source outside of the system and the generator output.
In another example, this document discusses a method of providing an electrical AC output signal to a first load. In this method, a first approximately DC voltage is generated from a fuel. The first DC voltage is modulated into the AC output signal. The AC output signal is provided to the first load. A limited amount of energy is transferred from an energy storage device onto the first DC voltage. The energy amount is substantially limited to that needed to maintain the first DC voltage at a first predetermined DC voltage value while the first load draws surge power AC output signal.
In another example, this document discusses a method of providing AC electrical power to a first load. In this method, a first load is decoupled from a utility-provided AC power source upon detecting a fault condition at the utility-provided AC power source. A DC voltage is modulated to provide backup AC power. The backup AC power is coupled to the first load when the first load is decoupled from the utility-provided AC power source. The generator is turned on to provide energy to the DC voltage. Energy is transferred from an energy storage device to the DC voltage during a time from the turning on of the generator to a time at which the generator is supplying sufficient power to maintain the DC voltage at a first predetermined voltage value. Other aspects of the invention will be apparent on reading the following detailed description and viewing the drawings that form a part thereof.